There’s only one thing I can think of that extreme heat is good for, and that is killing plants. And every so often, that’s exactly what we want to do. Do you have an infestation of deep-rooted noxious invasive weeds in your garden (Canada Thistle, Campanula rapunculoides aka ‘cancer of the garden’, bindweed, burdock, etc.)? The most effective time to apply 20% vinegar, or ‘Avenger’ and other citrus-oil weed-killers is during a hot day when plants are already stressed. Are you wishing to change your water-guzzling lawn into a low-water garden? Then this is an excellent time of year to ‘solarize’ your lawn.
Solarizing: This method essentially cooks the lawn and weeds and is most effective in full sun areas when
weather is very warm or hot. Depending on conditions, it can take 4 to 8 weeks, occasionally longer, to complete. The heat generated will cause a temporary reduction in soil biology, but this can be recovered at completion by adding compost tea, compost, and mycorrhizae.
1- Find a source of heavy 10-mil clear plastic ‘mulch’ (some hardware stores carry rolls or sell by the yard) and plan the area(s) you will treat to match the dimensions of the plastic, including 5” on each side for burying the edges.
2- Cut grass as low as possible. Clippings can be left in place unless they contain grass or weed seeds.
3- Apply high-nitrogen granular fertilizer and water thoroughly. You can us Corn Gluten in addition to inhibit weed-seed germination and add more nitrogen.
4- Dig a trench 2” deep and 4-5” wide around the area to be solarized. Keep the soil removed handy.
5- Cover the area with a single layer of plastic, pulled taut, and lay the edges in the surrounding trenches.
6- Place stones or bricks over the plastic in the trenches at intervals and fill in the rest of the trenches with the reserved soil. This should seal the area and keep the hot air from leaking out.
Before removing the grass, Save your trees: the water, air and nutrient-absorbing roots are close to the surface. When you remove lawn, you will damage some of these roots. It is often better to remove grass under a tree with a flat shovel so fewer roots are damaged. Removing grass under trees in cooler weather is also better since the tree will be transpiring less to cool itself. Also better to deep water and give liquid organic fertilizer one to two weeks before removing sod to give a tree extra strength to endure the stress. A liquid mycorrhizae may be helpful in re-establishing a root system.
Also, do not bury tree roots under more than 3”-4” of mulch (as in the Lasagna Method) since too much mulch can reduce oxygen to the roots and/or support root decay and fungal or bacterial diseases.
In addition: especially if the new garden will be water-wise, make sure the tree has its own irrigation system or is watered deeply twice a month. It takes years and years to grow back a tree and trees often need more water than native shrubs and forbs.